Blade lock

ABSTRACT

A turbomachine having a rotor assembly construction wherein a deformable blade lock is inserted in the clearance between the blade root and a slot in the periphery of a disc, the blade lock moving under the influence of centrifugal force in such a manner so as to prevent axial movement of the blade root in the disc slot.

United States Patent Inventor Gerard Muller Morristown, NJ. Appl. No.859,423 Filed Sept. 19, 1969 Patented Aug. 10, 1971 Assignee UnitedAircraft Corporation East Hartford, Conn.

BLADE LOCK 2 Claims, 3 Drawing Figs.

U.S. Cl Int. Cl t Field of Search 416/221 Fold 5/32 416/220,

[56] References Cited UNITED STATES PATENTS 2,641,443 6/1953 Comery eta1. 416/221 2,786,648 3/1957 Ledwith 416/221 2,828,942 4/1958 McCulloughet a1. 416/221 Primary Examiner-Everette A Powell, Jr. Allamey.CharlesA. Warren ABSTRACT: A turbomachine having a rotor assembly constructionwherein a deformable blade lock is inserted in the clearance between theblade root and a slot in the periphery of a disc, the blade lock movingunder the influence of centrifugal force in such a manner so as toprevent axial movement of the blade root in the disc slot.

BLADE LOCK BACKGROUND OF THE INVENTION This invention relates to bladelockfor a rotor assembly for use in a turbomachine.

It is obvious that in a turbomachine some arrangement must be providedto hold or lock the, blades in place inthe rotor assembly. One of themost commonmethods of retaining blades in a compressor or turbine that.is employed byprior art constructions is the use of keysor .tablockswhich lie beneath-the root of the blades at the bottom of the bladelocks and are fixed to the disc and blade. However, when the supportingdisc has a number of axially extending recesses in its periphery, toreceive the roots of the blades which zproject radially outward from thedisc, it becomes necessary to prevent axial movement of the bladerelative to. the disc because of .the axial thrust exerted on theblade.duringoperationof thecompressor or turbine. One of the inherentandbasic disadvantages of the prior art key-or tab'lock constructions isthat-these constructions are weak in the axial direction'with the resultthat the blades may walk out of the disc slots. Typical prior art constructions which have this inherent disadvantageare shown-in U.S. Pat.No. 2,828,942 and U.S. Pat. No. 3,383,095.

SUMMARY OFZTHE INVENTION It is a primary object of this inventiontoprovidea rotor assembly with a blade lock construction.whichpreventsmovement of the blade root in the disc inthe axial directiomparticularlyduring rotation ofthe rotor assembly.

The present invention relates to a deformable tab lock -posi-- tioned inthe radial clearance between the base of the'blade root and the slots inthe outer periphery of the rotor disc. The tab lock comprises flat stripmember which extends-axially in the slot in the rotor disc.ndincludestab or flange means on either end of the flap strip. Thedownstream tab projects radially outward, while the upstream tabprojectsradially inward, the downstream tab lockingagainst the bladeroot while the upstream tab locks against thedisc.

The flat strip member extending axially in the disc slot includes acontact means. This.contact means which is within the clearance betweenthe disc periphery and the blade root comprises an outwardly extendingresilient offset or hump which contacts the base surface of thebladeroot. The point of contact between the tab lock or contact meansand the blade root is of significance in that it is offset orasymmetrical with respect to the blade axis and the central plane of thedisc. The importance of this contact point being symmetricalv is that asthe discrotor gains speed, both the tab rotate about the contact point.More specifically, the downstream tab will, as a result the centrifugalforce, rotate counterclockwiseabout the contact point in an outwarddirection; whereas, theupstream flange will rotate clockwiseabout thecontact point. Since the contact point is asymmetricahthe offset beingin the upstream direction. the downstream or outwardlyextendingflangm-will rotateor deform a greater amount around the contactpoint than the inwardly extending upstream.flange-Therefore, as a resultof this deformation caused by centrifugal force, and as a result of themovement of these flanges, the blade root is locked more securelywithin-the slot of the rotor disc, thereby preventing axial movement ofthe root as the rotor disc speeds up.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an axial sectional viewthrough a disc showing the blade lock.

FIG. 2 is a sectional view along line 2-2 of FIG. I;

FIG. 3 is an axial scctionalyiew througha disc showing the blade lock inits deformed position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is 'showninconjunction with acompressor disc for use in a multistage axial 'flowcompressor construction, but it will be apparent that'theinvention isequally applicable to the fastening of blades in the discs of axial flowturbines or other similar apparatus. In the arrangement shown, thecompressor disc 2 which may have axially projecting flanges 4 thereonfor spacing'disc 2 from adjacent similar discs for other stages'of thecompressor has a plurality of axially extending slots 6' in itsperiphery to receive the similarly formed root 8 of the blade 10. Theparticular shape of the blade root or of the similarly shaped'disc-6 isnot critical. For the purpose of the present invention a slot is shownhavinga relatively broad base opening :12, the' base surface 14 of whichis substantially flat, a narrow neck l6'and broad outer end portion 18.The narrow neck 16 constitutes an outer peripheral portion of the slotradially outwardof the base opening. The blade root is similarin'shapehaving a broad base portion 20,-the

base surface 22 of which is substantially flat and is preferably of sucha dimension as to leave when the blade root is assembled in the slot, aclearance space of substantially uniform depth between the surface 2 ofthe root and the surface 14 of the slot for the insertion of the bladelock 24.

As best shown-in FIGS. 1 and 3, the blade lock is in a form of a thinflat strip 29 which is several times wider than its thickness andwhich'extends in an axial direction within the slot between the basesurface 14 of the slot and the base surface 22 of the blade root. Thestrip is thinner than the radial depth'of the slot to permit movement ofportions of the strip radially in the slot as will be described. In adirection transversely of the strip the latter is parallel to the basesurfaces of the blade root and slot, and these surfaces are preferablyat right angles to the plane ofthe disc. The strip is long enough toprovide material projecting beyond the ends of the slot to form firsttab-30and second tab 32. As illustrated tab 30 is the downstream tab andis bent outwardly'with respect to the axis of the disc to overlie theend of the blade root. Meanwhile tab 32 is the upstream tab and thistabis bent inwardly with respect to the axis of the' disc to overlie theside surface of the disc.-

The flat strip member 29 also includes a contact means34 whichextendsbetween the flat stripmember 29 and the base surface 22 of theblade root. Contact means 34 includes a resilient curved offset or humpformed to project outwardly'in the flat strip member 29. The contactmeans 34 contacts the base surface 22 at a point 36 which is offsetaxially from the central plane 38 of the disc in an upstream direction.More specifically, the contact point 38 is asymmetrical with respect tothe central plane of the disc 38and the axis of the blade.

As hereinbefore noted, flat strip member 29 includes first tab 30andsecond tab 32-. As the-rotor disc attains speed, both tabs, that is,tab 30 and tab 32, will, through centrifugal force and deformation,rotate about contact point 36. Morespecifi cally, tabv30will-rotateabout contact point 36 'a greater amount than tab 32 becauseof the asymmetrical or offset position of contact point 36 thetab 30being spaced farther fromthe'pivot pointthan the tab 32. Therefore. as aresult of this rotation or deformation ofthe tab lock, tab lock 30 movesoutwardly while tab lock 32 moves inwardly, the combined deformation ofthe tabs 30' and 32 locking the'blade root withinthe slot in a moresecure fashion so as to prevent any axial-movementtherein. FIG. 3clearly illustrates the locking technique of the constructionhereinbefore described with the blade lock in the position itassumes-during operation of the rotor at design speed.

Iclaim:

1. A rotor assembly for a turbomachine comprising a disc having rootreceiving slots extending transversely of the disc at its periphery, andblades having roots corresponding substantially in shape to and engagingin said slots, the base of each blade root being spaced radiallyfrom'the base of the slot to define clearance therebetween, wherein theimprovement comprises;

a deformable blade lock comprising a substantially flat resilient strippositioned in said clearance, the flat strip including a hump thereinextending between the blade root and disc periphery, the hump being incontact with the blade root at a point offset with respect to thecentral plane of the disc, and an integral tabs at each end of the flatstrip one of said tabs extending radially outward and engaging with theend of the blade root and the other tab extending radially inwardly tooverlie the side of the disc thereby to lock the blade root againstaxial movement in the disc, the contact between the blade root and thehump being offset from the central plane in an upstream direction.

2. A rotor construction for a gas turbine engine comprising a dischaving root receiving slots extending transversely of the disc at itsperiphery, and blades having roots corresponding substantially in shapeto and engaging in said slots, the base of the blade roots being spacedradially from the slot to define thinner than and positioned in saidclearance, the flat strip having an' offset therein extending outwardlybetween the blade root and disc periphery, the Offset being in contactwith the blade root at a point spaced upstream with respect to thecentral plane of the disc said strip having a first tab at the upstreamend thereof to overlie the side surface of the disc and a second tab atthe downstream end thereof to overlie the end of the blade root each tabbeing connected to the flat strip and being movable in response tocentrifugal force, the movement of the downstream tab being greater thanthe movement of the upstream tab by reason of the greater distance fromthe contact point between the offset and the blade root about which thestrip pivots under centrifugal force.

1. A rotor assembly for a turbomachine comprising a disc having rootreceiving slots extending transversely of the disc at its periphery, andblades having roots corresponding substantially in shape to and engagingin said slots, the base of each blade root being spaced radially fromthe base of the slot to define clearance therebetween, wherein theimprovement comprises; a deformable blade lock comprising asubstantially flat resilient strip positioned in said clearance, theflat strip including a hump therein extending between the blade root anddisc periphery, the hump being in contact with the blade root at a pointoffset with respect to the central plane of the disc, and an integraltabs at each end of the flat strip one of said tabs extending radiallyoutward and engaging with the end of the blade root and the other tabextending radially inwardly to overlie the side of the disc thereby tolock the blade root against axial movement in the disc, the contactbetween the blade root and the hump being offset from the central planein an upstream direction.
 2. A rotor construction for a gas turbineengine comprising a disc having root receiving slots extendingtransversely of the disc at its periphery, and blades having rootscorresponding substantially in shape to and engaging in said slots, thebase of the blade roots being spaced radially from the slot to defineclearance between the blade root and disc periphery, wherein theimprovement comprises; a deformable blade lock comprising asubstantially flap strip thinner than and positioned in said clearance,the flat strip having an offset therein extending outwardly between theblade root and disc periphery, the offset being in contact with theblade root at a point spaced upstream with respect to the central planeof the disc said strip having a first tab at the upstream end thereof tooverlie the side surface of the disc and a second tab at the downstreamend thereof to overlie the end of the blade root each tab beingconnected to the flat strip and being movable in response to centrifugalforce, the movement of the downstream tab being greater than themovement of the upstream tab by reason of the greater distance from thecontact point between the offset and the blade root about which thestrip pivots under centrifugal force.